Change in kinetic energy Velocity not given

[rock_star]

change in kinetic energy! Velocity not given :(

Homework Statement

Two forces, of magnitudes F1 = 70.0 N and F2 = 35.0N , act in opposite directions on a block, which sits atop a frictionless surface, as shown in the figure. Initially, the center of the block is at position xi = -2.00cm . At some later time, the block has moved to the right, and its center is at a new position, Xf = 4.00 cm .

Determine the change in the kinetic energy of the block as it moves from Xi= -2.00 to X f= 4.00

Link to the diagram : http://session.masteringphysics.com/problemAsset/1011314/13/MWE_wi_5.jpg

Homework Equations

Kinetic energy = 1/2 mv^2

The Attempt at a Solution

Since it is starting from rest, initial velocity, V0 = 0 and then d = Vf t

But here Vf is not given..
I am not sure how to proceed when there is no velocity given

Can any more help me ?

Thanks a lot before hand

 

[berkeman]

Homework Statement

Two forces, of magnitudes F1 = 70.0 N and F2 = 35.0N , act in opposite directions on a block, which sits atop a frictionless surface, as shown in the figure. Initially, the center of the block is at position xi = -2.00cm . At some later time, the block has moved to the right, and its center is at a new position, Xf = 4.00 cm .

Determine the change in the kinetic energy of the block as it moves from Xi= -2.00 to X f= 4.00

Link to the diagram : http://session.masteringphysics.com/problemAsset/1011314/13/MWE_wi_5.jpg

Homework Equations

Kinetic energy = 1/2 mv^2

The Attempt at a Solution

Since it is starting from rest, initial velocity, V0 = 0 and then d = Vf t

But here Vf is not given..
I am not sure how to proceed when there is no velocity given

Can any more help me ?

Thanks a lot before hand

What is the net force acting on the block? Just keep the mass and velocity as variables, m and V for now. Write the equations to tell you how long it takes to get to the 2nd position, and what the final velocity is. Then see if some of the variable terms cancel out...

 

[rl.bhat]

Change in kinetic energy = work done on the block = Force X displacement.
In the problem force and displacement is given. That is sufficient to find the KE.

 

[rock_star]

Thank a lot everyone! :)
I understood it! :D
Thank a ton everyone!